The invention herein relates to a crankshaft impact protector which protects the crankshaft of a lawnmower combustion engine from bending beyond its elastic limit. The crankshaft impact protector disclosed herein also provides a mounting base whereupon the lawnmower combustion engine can be mounted. Further, the disclosed crankshaft protector helps to prevent soil and dust from reaching the crankshaft seal thereby preventing premature failure.
Prior art rotary lawnmowers are generally constructed with a combustion engine having a substantially vertically disposed crankshaft extending downward through the mower deck. A cutting blade is bolted directly to the bottom of the crankshaft so that it can rotate therewith. It is known that the striking of a hard or immovable object such as a rock or a stump by the cutting blade can bend the crankshaft while it is absorbing the impact and, further, can cause additional internal engine damage because of transmission by the crankshaft to the engine of the impact forces. Naturally, the bent crankshaft causes the lawnmower to be substantially nonfunctional and, therefore, the crankshaft must then be straightened or replaced. However, this is undesirable because replacing or straightening the crankshaft is generally comparatively expensive.
Accordingly, there is a need for a device which can absorb the impact forces from the crankshaft whenever a hard or immovable object is struck by the cutting blade such that the crankshaft is prevented from bending beyond its elastic limit. Further, there is a need to provide this device inexpensively and without adding undue weight to the lawnmower.
In the past, crankshafts have been protected from impact forces by adding a third ball bearing or sleeve bearing to the engine substantially near the end of the crankshaft. An example of this design is illustrated in U.S. Pat. No. 3,420,042. However, this design is undesirable because it significantly adds to the cost of the lawnmower and also substantially increases the overall weight.
Other attempts to protect lawnmower crankshafts from impact forces have involved the use of an additional stamping or casting mounted underneath and onto the mower deck whereby the crankshaft is prevented from deflecting beyond its elastic limit. Examples of this design are illustrated in U.S. Pat. Nos. 2,940,241 and 3,065,589. This design is also undesirable becuse the cost and the weight of the lawnmower are significantly increased. Further, this design is undesirable because it is difficult to maintain a uniform clearance between the crankshaft and the casting or stamping center bore. When an impact force is experienced, the casting or stamping frequently shifts from its original mounting position thereby resulting in contact or rubbing between the crankshaft and the center bore. Naturally, when this occurs, the casting or stamping must be recentered at a considerable cost and inconvenience to the operator.